To: rsgb_lf_group@blacksheep.org
Date: Tue, 12 Oct 2010 14:57:48 -0400
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From: Markus Vester <markusvester@aol.com>
Message-Id: <8CD38567F4B0C6A-1C1C-116D@webmail-m021.sysops.aol.com>
Subject: VLF: Detections of 5 microwatt transmission
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Dear LF,

for my VLF test transmissions on the last weekend (Oct 9: 8969.998 Hz, Oct=
. 10: 8989.997 Hz), I have received reports from three receiving stations:

- Walter DJ2LF near Erlangen (20.2 km) received the carrier again in good=
 quality, using 0.95 mHz resolution. Radiated power and received SNR were=
 quite similar to our two-way QSO on June 4th.

- Stefan DK7FC in Heidelberg (178.5 km) reported about 10 dB SNR, and both=
 dashes are still visible in the QRN minima on his 47uHz grabber window=20

http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html

This was the intended purpose of the experiment, and a nice counterpart to=
 the earlier detection of a 200 uW kite transmission on Aug 29th. Even tho=
ugh both of us were locking the samplerate to a 10 kHz GPS-derived referen=
ce, the dashes appeared about two pixels low - perhaps due to a very minut=
e rounding error in SpecLab's frequency scale display.

- To my utter surprise, Paul Nicholson (Todmorden, 1030.5 km) produced two=
 spectra, taken over the duration of the transmissions:

   http://abelian.org/vlf/df6nm/2010_10_09a.gif   (9:50 - 18:00, 34 uHz)
   http://abelian.org/vlf/df6nm/2010_10_10a.gif   (9:00 - 15:00, 46 uHz)

After taking a deep breath, we now have to deal with the question whether=
 this is a significant positive detection. Except for a known central arti=
fact on 8970, the highest peak appears in the correct frequency bin in bot=
h spectra. Naively, one could then propose that the probability of this ha=
ppening at random would simply be the inverse of the number of displayed=
 bins, ie. around 1:230 for Saturday and 1:170 for Sunday. Thus the combin=
ed probability of a false positive detection on both days would seem to be=
 only 1 in 40000. Certainly there is a degree of arbitrariness in the choi=
ce of the display range (8 mHz).

Paul estimated that the signal was about 3 standard deviations on Saturday=
 (0.3% false detection rate), and 2 sigma in the higher noise on Sunday (5=
%), giving a combined false positive probability of 1 in 6667.

We can also look at the plausibility of the absolute fieldstrength of the=
 peaks (about 0.2 fT, equivalent to 0.06 uV/m). If I remember correctly,=
 Paul's first detection of Stefan's kite signal on March 15 was at about=
 3 fT, and Stefan was then radiating approx. 1 mW EMRP. Scaling this down=
 to my estimated 5 uW EMRP, and taking another dB for the slightly higher=
 distance, would theoretically result in 24 dB less fieldstrength, or 0.19=
 fT - almost a perfect match.

So by these lines, it would seem at least very likely that Paul has indeed=
 observed my feeble signal! We intend to do repeat the experiment in the=
 near future for additional confirmation.

Very many thanks to all involved in this work!

73, Markus (DF6NM)

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<font color=3D'black' size=3D'2' face=3D'arial'>
<div><br>
Dear LF,</div>


<div>&nbsp;</div>


<div>for my VLF test transmissions on the last weekend (Oct 9: 8969.998 Hz=
, Oct. 10: 8989.997 Hz), I have received reports from three receiving stat=
ions:</div>


<div>&nbsp;</div>


<div>- Walter DJ2LF near Erlangen (20.2 km) received the carrier again in=
 good quality, using&nbsp;0.95 mHz resolution. Radiated power and received=
 SNR were quite similar to our two-way QSO on June 4th.</div>


<div>&nbsp;</div>


<div>- Stefan DK7FC in Heidelberg (178.5 km) reported about 10 dB SNR, and=
 both dashes are still visible in the QRN minima on his 47uHz grabber wind=
ow </div>


<div>&nbsp;</div>


<div><A href=3D"http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Gr=
abber.html">http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabbe=
r.html</A></div>


<div>&nbsp;</div>


<div>This was the&nbsp;intended purpose of the experiment, and&nbsp;a nice=
 counterpart to the earlier detection of a 200 uW kite transmission on Aug=
 29th. Even though both of us were locking the samplerate to a 10 kHz GPS-=
derived reference, the dashes appeared about&nbsp;two pixels low - perhaps=
 due to a very minute rounding error in SpecLab's frequency scale display.=
</div>


<div>&nbsp;</div>


<div>- To my utter surprise, Paul Nicholson (Todmorden, 1030.5 km)&nbsp;pr=
oduced two spectra, taken over the duration of the transmissions:</div>


<div>&nbsp;</div>


<div>&nbsp;&nbsp; <A href=3D"http://abelian.org/vlf/df6nm/2010_10_09a.gif"=
>http://abelian.org/vlf/df6nm/2010_10_09a.gif</A>&nbsp;&nbsp; (9:50 - 18:0=
0, 34 uHz)<br>
&nbsp;&nbsp; <A href=3D"http://abelian.org/vlf/df6nm/2010_10_10a.gif">http=
://abelian.org/vlf/df6nm/2010_10_10a.gif</A>&nbsp;&nbsp; (9:00 - 15:00, 46=
 uHz)</div>


<div>&nbsp;</div>


<div>After taking a deep breath, we now have to deal with the question whe=
ther this is a significant positive detection. Except for a known central=
 artifact on 8970, the highest peak appears in the correct frequency bin=
 in both spectra. Naively, one could then propose that the probability of=
 this happening at random would simply be the inverse of the number of dis=
played bins, ie. around 1:230 for Saturday and 1:170 for Sunday. Thus the=
 combined probability of a false positive detection on both days would see=
m to be only 1 in 40000. Certainly there is a degree of arbitrariness in=
 the choice of the display range (8 mHz).</div>


<div>&nbsp;</div>


<div>Paul estimated that the signal was about 3 standard deviations on Sat=
urday (0.3% false detection rate), and 2 sigma in the higher noise on Sund=
ay (5%), giving a combined false positive probability of 1 in 6667.</div>


<div>&nbsp;</div>


<div>We can also look at the plausibility of the absolute fieldstrength of=
 the peaks (about 0.2 fT, equivalent to 0.06 uV/m). If I remember correctl=
y, Paul's first detection of Stefan's kite signal on March 15 was at about=
 3 fT, and Stefan was then radiating approx. 1 mW EMRP. Scaling this down=
 to my estimated 5 uW EMRP, and taking another dB for the slightly higher=
 distance, would theoretically result in 24 dB less fieldstrength, or 0.19=
 fT - almost a perfect match.</div>


<div>&nbsp;</div>


<div>So by these lines, it would seem at least very likely that Paul has=
 indeed observed my feeble signal! We intend to do repeat the experiment=
 in the near future for additional confirmation.</div>


<div>&nbsp;</div>


<div>Very many thanks to all involved in this work!</div>


<div>&nbsp;</div>


<div>73, Markus (DF6NM)<br>
</div>
</font>

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